In U.S. Pat. No. 4,948,948, there is described a water heater with multiple heating elements having different power factors and wherein these elements are controlled by a control circuit so that the elements are switched on at different periods of a day, outside peak hours, in order to reduce the power loads on an electrical distribution network during peak electrical power demand periods. During peak hours when hot water is used, normally between 6:00 a.m. and 9:00 a.m. and 6:00 p.m. to 9:00 p.m., there is an excessive demand of power on the electrical distribution network. Electrical utilities have been searching for adequate solutions to this problem and one such solution is to increase the cost of electricity during peak periods of time thereby forcing consumers to use hot water at different periods of time whereby to try and reduce the demand during peak power periods. Another solution is for utilities to control the domestic circuits branched to high power rated appliances during this peak period of time and such controls have to be done remotely or with timers. These solutions are, however, costly to the utilities and are not popular with consumers. They also cause very high instantaneous demand when they are re-activated if too many units are turned back in at the same time. The patent referred to hereinabove also discusses other attempts by utilities to control power consumption during peak demand periods and some of these solutions can be very troublesome.
As described in U.S. Pat. No. 4,948,948 the resistive elements are of different power ratings with the top one of the elements being the highest power rated for heating a small volume of water in the top portion of the reservoir where water is drawn out of the tank to maintain the water in top portion at the set hot water temperature. However, during peak periods of time the amount of water in the top portion of the reservoir is quickly exhausted as it has been found that many consumers will draw hot water during a single peak period of the day rather than two separate periods and therefore demand a much larger hot water volume.